Polyolefin products and process additives therefor having reduced transfer to substrates

ABSTRACT

A process additive for polyolefin films and foams produces products having reduced aging time and reduced greasiness and reduced grease-like transfer as compared to glycerol monostearate (GMS). Carbon dioxide based blowing agents are suitable. The process additive comprises a fatty acid N-aliphatic alcohol amide of the general formula R—CON(R′)R″. R is a fatty hydrocarbon radical having from about 8 to 30 carbons. R′ typically is hydrogen. R′ can also be an alkyl radical of from about 1 to 6 carbons or an alkyl alcohol radical of from about 1 to 6 carbons. R″ is an alkyl alcohol fragment of from about 1 to 6 carbons. The alkyl alcohol fragments can be monohydric or polyhydric. Secondary fatty monoalkanolamides in which R′ is hydrogen are particularly useful, especially stearamide monoethanolamine (MEA). The benefits of the invention can be achieved and enhanced in some examples by mixing the fatty acid N-aliphatic alcohol amide with an ester of a long chain fatty acid with a polyhydric alcohol, including GMS. Examples of fatty acid N-aliphatic alcohol amides include cocamide MEA, lauramide monoisopropylamine (MIPA), oleamide MIPA, and stearamide 2,3-propanediol.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of copendingapplication Ser. No. 08/944,732, filed Oct. 6, 1997, incorporated hereinby reference in its entirety, and claims the benefit of its earlierfiling date.

FIELD OF THE INVENTION

[0002] This invention relates to products made from polyolefins andprocess additives used in connection therewith. In particular, thisinvention relates to extrudable compositions for producing polyolefinfilms and to expandable compositions for producing polyolefin foamproducts.

BACKGROUND OF THE INVENTION

[0003] Various processes and equipment for extrusion foaming ofthermoplastic resins have been used for many years. Generally, solidpellets of thermoplastic resin are fed through a hopper to a meltingzone in which the resin is melted, or plasticized, to form a flowablethermoplastic mass. The plasticized thermoplastic mass generally is thentransported to a mixing zone where the thermoplastic mass is thoroughlymixed with a blowing agent under pressure for subsequent cooling andsubstantially free expansion of the resin to form a foam.

[0004] The blowing agent expands the molten mass to form the cells ofthe foam and the thermoplastic foam is cooled.

[0005] The blowing agent gradually diffuses from the cells of the foamand is eventually replaced by air diffusing into the cells. Diffusivityof the blowing agent and the selection and use of appropriate blowingagents are important aspects of foam manufacture. If the diffusivity ofa blowing agent out of the cells of a foam is too fast compared to thediffusivity of air, so that the blowing agent is not replaced by air asit escapes, then the foam typically collapses and is said to havedimensional stability problems. For many years, chlorofluorocarbons(“CFCs”) were used that had excellent diffusivity characteristics andresulted in high quality, dimensionally stable foam products. However,CFCs are no longer acceptable as blowing agents because of globalregulations prohibiting their use.

[0006] Other compounds, including lower hydrocarbons, alcohols andketones, various hydrofluorocarbons, and inert gases have been proposedas alternative blowing agents to CFCs. Some of these compounds diffuseout of the foam cells at a rate that reduces dimensional stability andcan result in collapse of the foam cells. Aging modifiers have beendeveloped for incorporation into polyolefin resins that slow thediffusion of selected blowing agents out of the polyolefin foam cells.These aging modifiers are sometimes referred to as permeabilitymodifiers or stability control agents. Among the various aging modifiersthat have been proposed are the saturated higher fatty acid amides,saturated higher aliphatic amines, esters of saturated higher fattyacids, copolymers of ethylene and unsaturated carboxylic acids, andothers.

[0007] One of the more widely used aging modifiers for polyolefin foamsis glycerol monostearate. Glycerol monostearate is also added to resinsfor extrusion to form films. Glycerol monostearate is also called GMS,glyceryl monostearate, and monostearin. GMS is a monoglyceride and is anester of stearic acid, which is C₁₈ acid, and the trihydric alcoholglycerol. GMS is a pure white or cream colored and wax-like solid.

[0008] GMS and other similar aging modifiers are thought to coat thewalls of the foam cells to slow the blowing agent gas from escaping andthereby to prevent collapse of the cells of the foam. However, theseaging modifiers can leave a grease-like residue on the surface of thefoam that can be transferred to objects that come into contact with thefoam. The transfer of this grease-like residue to certain substrates isproblematic and is particularly undesirable on optical products and highgloss finishes.

[0009] GMS also tends to slow the rate of blowing agent diffusion fromthe cells to the point that some residual blowing agent is maintained inthe cells for an undesirably long period of time after manufacture. Tooslow a rate of blowing agent diffusion from the cells of the foam canresult in dimensional stability problems. Foam rolls can become tight instorage.

[0010] It would be desirable to provide a foam product in which anacceptable blowing agent would escape from the cells of the fresh foamat a rate that more closely matches the rate of air entering the cellsof the foam to substantially eliminate dimensional changes in the foamupon aging. It would also be desirable to provide foam and otherproducts, including films, in which transfer of grease-like residue tosubstrates is reduced.

SUMMARY OF THE INVENTION

[0011] The invention relates to process additives for polyolefinproducts that can substantially reduce greasy deposits on substratesand, in foams, promotes an increased rate of escape of blowing agentfrom the cells as compared to glycerol monostearate (GMS) alone. Theprocess additives are particularly useful for producing stable foamsfrom carbon dioxide based blowing agents and reducing the aging time forthese foams. The process additive comprises at least one fatty acidN-aliphatic alcohol amide and can be a secondary or tertiary amide.

[0012] An ester of a long chain fatty acid with a polyhydric alcohol,including GMS, can be used with the amide, while still achieving thebenefits of the invention. The two components can be added to thepolyolefin resin either in admixture or separately. The amide and theester have been observed to exhibit a substantially single differentialscanning calorimetry (DSC) melting point that varies linearly dependingon the relative amounts of amide and ester, thus signifying somechemical compatibility. It has also been observed that the transfer ofgrease-like residue is more substantially reduced when both the esterand the amide are present in the polyolefin resin than when the amide isused in the absence of the ester.

[0013] Typically the ester and the amide are present in the processadditive in a ratio of the ester to the amide of from about 0:1 to 10:1.The polyolefin and process additive typically are present in a ratio offrom about 100:0.01 to 100:5, respectively.

[0014] The fatty acid N-aliphatic alcohol amide is a secondary ortertiary amide having the formula R—CON(R′)R″. R is a fatty hydrocarbonradical having from about 8 to 30 carbons. R′ typically is hydrogen. R′can also be an alkyl radical of from about 1 to 6 carbons or an alkylalcohol radical of from about 1 to 6 carbons. R″ is an alkyl alcoholfragment of from about 1 to 6 carbons. The alkyl alcohol fragments canbe monohydric or polyhydric. Secondary fatty monoalkanolamides, in whichR′ is hydrogen and which have the general formula RCONHR″, areparticularly useful process additives.

[0015] One method of preparing the amide is to react a fatty acid withan alkanolamine, especially a monoalcohol amine. The amine group of thealkanolamine is substituted for the hydroxyl moiety of the fatty acidcarboxyl group to form a molecule having a fatty acid amide moiety andan aliphatic alcohol moiety characterized by the attachment of thealcohol moiety to an amide nitrogen. The fatty acid is typically coconutacid, lauric acid, stearic acid, palmitic acid, or oleic acid. Thealkanolamine is typically monoethanolamine (MEA), monoisopropanol amine(MIPA), n-propanolamine, betapropanolamine, or 2,3-propanediol amine. Anexample is the fatty monoalkanolamide stearyl monoethanolamide, whichhas the formula CH₃(CH₂)₁₆CONHCH₂CH₂OH and is sometimes calledstearamide MEA. Another example, in which the alcohol is dihydric, isstearyl 2,3-dihydroxy propyl amide, which is also called stearamide2,3-propanediol and which has the formula CH₃(CH₂)₁₆CONHCH₂CH(OH)CH₂OH.

[0016] The invention includes polyolefinic compositions that are filmsor foams and compositions for preparing polyolefin foam products inwhich the above process additive is incorporated. Typically, the resinis selected from the group consisting of ethylene or propylenehomopolymers and copolymers of ethylene or propylene and acopolymerizable monomer. Stable foams having a relatively short agingtime can be prepared from carbon dioxide blowing agents, includingblends of carbon dioxide with hydrocarbons, including the volatilehydrocarbons.

[0017] The invention includes a polyolefin foam product that comprisesan expanded polyolefin made from the foamable composition describedabove. Grease-like transfer to substrates is substantially reduced ascompared to GMS alone. Aging time is significantly reduced without lossof stability. Sheet products are useful because sheet products are mosttypically used to protect high gloss finishes, optical products, and thelike. However, the invention is also applicable to plank foam productsand to films.

[0018] Thus the invention provides a process additive that can functionas an effective aging modifier, a foamable composition containing theprocess additive, and a polyolefinic foam made from the foamablecomposition. The foam exhibits reduced grease-like transfer tosubstrates and is dimensionally stable. Aging time is significantlyimproved and can be reduced by as much as half or more. Carbon dioxideblowing agents can be used. The invention also provides extrudablecomposititons and films made from them that incorporate a processadditive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Some of the features and advantages of the invention have beenstated. Other advantages will become apparent as the description of theinvention proceeds, taken in conjunction with the accompanying drawings,in which:

[0020]FIG. 1 is a plot of absorbence at various wavelengths for severalprocess additives at 2 percent concentration by weight in a 2 mil thickpolyethylene film, including a process additive according to theinvention;

[0021]FIG. 2 is a plot showing a concentration of glycerol monostearate(GMS) on the surface of a foam and as transferred to a highly polishedKBr window with which the foam has come into contact;

[0022]FIG. 3 is a plot showing the effect of an increase inconcentration of GMS in polyethylene foams on its absorbence at variouswavelengths;

[0023]FIG. 4 is a plot comparing the property of grease-like transferfor various process additives. A commercially available GMS is given thevalue of 1;

[0024]FIG. 5 shows that the grease-like transfer increases withincreasing concentration of GMS;

[0025]FIG. 6 is a plot comparing absorbance peaks for several processadditive compositions;

[0026]FIG. 7 is a plot comparing absorbance peaks for several processadditive compositions; and

[0027]FIGS. 8 and 9 are plots of the percentage of the lowest explosivelimit (% LEL) over time for polyethylene foams prepared with the processadditives of the invention.

DETAILED DESCRIPTION

[0028] Various compounds were evaluated quantitatively as processadditives for grease-like transfer to substrates by high performanceFourier-transform infrared spectroscopy (FT-IR). Plots are shown inFIGS. 1 through 3, 6, and 7 of the fraction of absorbence in themid-infrared region for particular compounds of interest. Infraredradiation is recorded in the customary units of wavenumbers, which areoscillations per centimeter and are read as reciprocal centimeters. Themid-infrared region of from about 200 to 4,000 cm⁻¹ corresponds towavelengths of light of from about 50 to 2.5 microns.

[0029] Spectroquality potassium bromide (KBr) crystal was chosen as auseful candidate for studying grease-like transfer from a foam surfaceto a glass-like or highly polished substrate. KBr crystal typically isused in FT-IR spectroscopy. KBr crystal absorbs no infrared light in thespectrum from 4000 to 400 cm⁻¹, which are the wavenumbers of interest.KBr crystal was used in all of the examples shown below except asotherwise noted, and is sometimes referred to below as “glass.”

[0030] Chemical formulas for various compounds that were analyzed byFT-IR spectroscopy, including a compound in accordance with theinvention, are shown below in Table 1 and are identified in the Figuresby letter codes A through H. Kemamide S-180(C), Kemamide S(D), AlkamideS-280(E), Alkamide L-203(F), and Alkamide LIPA are tradenames forvarious commercial products corresponding to the formulas and lettercodes as shown in Table 1. SAPD designates stearamide 2,3-propanediol.The Kemamides are available from Humko Chemical Division of WitcoCorporation, which is located in Memphis, Tennessee. The Alkamides areavailable from Rhone-Poulenc, which is located in Cranbury, N.J. SAPDwas made by and is available from Rhone-Poulenc by special request.Alkamide S-280, Alkamide L-203, Alkamide LIPA, and SAPD are all examplesof compounds useful as process additives in accordance with theinvention.

[0031] There are two principal grades of glycerol monostearate (GMS)used in the plastics industries as process additives, including agingmodifiers. One grade, identified below as “B” in Table 1, is derivedfrom hydrogenated tallow that contains about 65 percent stearic acidradicals and about 30 percent palmitic acid radicals. The tallow isesterified with glycerol and typically contains about 56 percentmonoester, 37 percent diester, and 7 percent of the triester. This gradeof GMS is what is typically referred to commercially as “GMS” or asglycerol mono/distearate. It is available from Witco Corporation, HumkoChemical Division, Memphis, Tennessee, under the designation Atmos 150.It is also available under the designation Pationic 1052, which is soldby the American Ingredients Company, Patco Polymer Additives Division,Kansas City, Mo.

[0032] Another grade of GMS is the distilled ester, d-GMS, which isidentified as “A” in Table 1, Distilled GMS typically contains about 96percent of the monoester. Distilled GMS is available under thedesignations Atmer 129 and Pationic 902 from Witco and Patco,respectively, whose locations are given above. TABLE 1 COMPOUND FORMULASLetter Code Name Formula R Group A Distilled Glycerol R-COOCC(OH)COHStearyl Monostearate, 96% B Glycerol Mono/distearate R-COOCC(OH)COH, 55%Stearyl (R-COOC)₂COH, 37% C Kemamide S-180 R-CONHR Stearyl D Kemamide SR-CONH₂ Stearyl B Alkamide S-280 R-CONH—C—C—OH Stearyl F Alkamide L-203R-CONH—C—C—OH Lauryl G Alkamide LIPA R-CONH—C—C(CH₃)OH Lauryl H SAPDR-CONH—C—C(OH)COH Stearyl

[0033] As can be seen from Table 1, compounds E and F, which are usefulas process additives in accordance with the invention, are stearyl- andlauryl-monoethanolamide, respectively. These compounds are also calledstearamide monoethanolamine (MEA) and lauramide MEA, respectively.Stearamide MEA can be represented by the formula CH₃(CH₂)₁₆CONHCH₂CH₂OH.Lauramide MEA can be represented by the formula CH₃(CH₂)₁₀CONHCH₂CH₂OH.

[0034] Compounds G and H are also useful as process additives of theinvention. Compound G is a lauryl monoisopropanol amide and is sometimesreferred to as lauramide monoisopropanolamine (MIPA). Compound H is anexample prepared from a dihydric alcohol amine, 2,3-propanediol amine.

[0035] These fatty monoalkanolamide compounds have the general formulaR—CON(R)R″, in which R is the stearyl or lauryl group, respectively, R′is H, and R″ is an alcohol moiety, ethanol, isopropanol, or2,3-propanediol moiety.

[0036] It is observed that complex molecules of the general formula havea hydrophobic end in the R group that is separated from a hydrophilicend in the R″ group. While not wishing to be bound by theory, it isbelieved that the distinct functionalities of the hydrophobic andhydrophilic portions of the compound may be at least partiallyresponsible for the favorable characteristics of these compounds asprocess additives, and, in particular, as aging modifiers.

[0037] Generally, the process additives of the invention that have thesedistinct hydrophilic and hydrophobic functionalities comprise at leastone fatty acid N-aliphatic alcohol amide. The substituted amide can beeither a secondary amide or a tertiary amide and typically will have theformula R—CON(R′)R″.

[0038] These compounds are complex molecules having an amide functionalmoiety and at least one alcohol functional moiety. These compounds arecharacterized by the aliphatic alcohol moiety R″ attached to an amidegroup nitrogen and a hydrocarbon group R attached to the carbon of theamide group.

[0039] R generally can be any fatty hydrocarbon group of from about 8 to30 carbons to provide a distinct hydrophobic component of the compound.The preferred fatty portion of the amide is lauryl, stearyl, palmityl,or oleyl, because these are the most economical to use. It should beunderstood that many commercial grades of fatty acids that may be usedto prepare the process additives of the invention are mixtures andtypically are not of one pure acid, even though these acids are commonlycalled by the predominant acid present. For example, commercial gradestearic acid typically has palmitic acid in it. Coconut acid, from whichcocamide MEA and similar compounds are derived, typically has a varietyof acid chain lengths present that vary from 6 to 18 carbons, but ismostly 10, 12, and 14 carbons.

[0040] R′ is selected from the group consisting of hydrogen, an alkylradical of from about 1 to 6 carbons, and an alkyl alcohol or glycolradical of from about 1 to 6 carbons, with the hydroxyl moiety on anycarbon in the group. Compounds in which R′ is hydrogen are useful andnormally are less expensive.

[0041] The aliphatic alcohol portion, R″, of the amide in Alkamide S-280and L-203 is an ethanol moiety. However, other alcohols, both monohydricand polyhydric, and having related properties and sufficient chainlength in the structure should be useful, although not necessarily withequivalent results. The alcohol provides a distinct hydrophilic portionof the compound and should not introduce a significant hydrophobicportion. For example, Alkamide LIPA and SAPD have an R″ portion ofisopropyl alcohol and 2,3-propanediol, respectively.

[0042] R′ and R″ can be any monohydric or polyhydric alkyl alcoholradical of from about 1 to 6 carbons. R′ usually is hydrogen and R″typically will be a monohydric or polyhydric alkyl alcohol moiety thathas from about 1 to 6 carbons. Typically a monohydric alkyl alcoholmoiety will be selected from the group consisting of methanol, ethanol,propanol, isopropanol, butanol, pentanol, and hexanol moieties, and inany isomeric form. A polyhydric alcohol moiety typically will beselected from the group consisting of glycols and glycerol. Ethanol,isopropyl, or dihyroxy propanol moieties are useful.

[0043] Typically, for economic reasons, the fatty acid N-aliphaticalcohol amide will be the reaction product of a fatty acid and analkanolamine. The fatty acid can be any of those having from about 8 to30 carbons, and will usually be either coconut acid, lauric acid,stearic acid, palmitic acid, or oleic acid. The alkanolamine can be aprimary amine, including ethanolamine, isopropanolamine, propanolamine,2,3-propanediol amine, betapropanolamine, and others.

[0044]FIG. 1 is a plot of mid-infrared absorbance at various wavenumbersfor several compounds B, C, D, and E as identified in Table 1. Theabsorption level changes with the thickness of the film sample and theinfrared absorption characteristics of the particular compound. However,the values shown on the plot of FIG. 1 have been normalized according tofilm thickness. The area under each peak corresponds to the amount ofthe compound that is present in the sample. FIG. 1 and similar plots canbe used as the basis for determining the relative grease-like transfercharacteristics of various compounds when used in foam production forapplication to glass-like and highly polished surfaces, as explainedfurther hereinbelow.

[0045] All of the compounds shown in FIG. 1 are at a two percentconcentration in a low density polyethylene resin that has been extrudedto a film. The peak at 1730 cm⁻¹ for compound B is for a film thatcontains commercial GMS process additive, which is typically used as anaging modifier and is also used as a slip agent for providing lubricityin the extruder. Three separate peaks are identified at 1650 cm⁻¹ forcompounds C, D, and E. The peak labeled E is for Alkamide S-280, whichis stearyl monoethanolamide and is an example of an aging modifier inaccordance with the invention in a low density polyethylene resin thathas been extruded to a film. Additional peaks are labeled C for KemamideS-180 and D for Kemamide S, each of which is in a low densitypolyethylene resin that has been extruded to a film.

[0046]FIG. 2 shows the foam surface peak and the glass transfer peak fora concentration of 1.2 percent of commercial grade GMS in a low densitypolyethylene resin that was extruded to form a foam of density 1.3pounds per cubic foot. The foam surface and glass transfer peaks, whichare at 1730 cm¹, correspond to a carbonyl group in the GMS structure.The large foam surface peak shows absorption in the infrared spectrumdue to the presence of GMS aging modifier on the foam surface. Thesmaller transfer peak shows absorption in the infrared spectrum that isdue to GMS aging modifier that has been transferred from the foamsurface to the KBr window; which provides a glass-like or highlypolished surface.

[0047] Quantitative measure of GMS on the surface of the foam and on thesurface of the window is obtained by integrating the area under thecorresponding peak. The ratio in the area calculated under the two peaksshows the amount of transfer from the foam surface to the window and isa measure of the grease-like transfer of the process additive from thefoam.

[0048] Table 2, below, shows data obtained in accordance with theprocedure outlined for FIGS. 1 and 2 that indicates the grease-liketransfer characteristics of a variety of process additives. The dataplotted in FIG. 2 corresponds to Example 7 in Table 2, which is acommercial grade GMS and is the benchmark for grease-likecharacteristics and grease-like transfer.

[0049] For each example in Table 2, a circular KBr window of one-inchdiameter was placed on the surface of a sample of a thin, light weightpolyethylene foam. The sample was maintained in an oven at 32°Centigrade for one day. A slight load of about 0.06 to 0.12 lb_(f)/in²was applied to the window to simulate packaging conditions in which aproduct having a glass-like or highly polished surface is packaged in athin, light weight polyethylene foam. Thereafter, the KBr crystal wasremoved from the oven and analyzed to show the amount of compoundtransferred to the surface of the crystal.

[0050] Each sample was subjected to FT-IR analysis and curves ofabsorbance versus wavenumber were generated. The area under the peak at1730 cm⁻¹ was integrated to calculate the amount of compound that wastransferred to the surface of the crystal. The ratio of the amount ofcompound transferred to the crystal surface to the amount of compoundoriginally on the surface of the foam was determined. This ratio wasthen multiplied by 100 to convert it into a percentage of transfer ofcompound from foam to glass. The above procedure was repeated for all ofthe compounds shown in Table 2. TABLE 2 Melting % Transfer % point of ofadditive % Example Foam Type Concentration additive from foam Greasiness% Reduction No. Additive (thickness) of Additive ° C. to glass Level inGreasiness Comments 1 B Black (⅛″) 0.4 60 16.1 66 34 Greasy# 2 B Black(⅛″) 0.4 60 5.7 24 76 Greasy 3 A White (.094″) 1.2 60 17.0 70 22 Greasy4 A White (.094″) 0.6 60 11.6 48 57 Greasy 5 A White (.094″) .043 60 9.439 61 Greasy 6 A White (0.08″) 0.3 60 8.9 37 56 Greasy 7 B White (.074″)1.2 60 24.2 100 0 Greasy 8 E White (.085″) 2.0 92 3.3 6 94 Good* 9 FWhite (.075″) 2.0 82 3.6 7 93 Good 10 F White (.091″) 2.0 82 2.6 5 95Good 11 H White (0.9″) 1.0 98 4.2 10 90 Good

[0051] The results calculated for the percent transfer of variousadditives from foam to glass is shown in Column 6 of Table 2. Thepercent transfer of additive from foam to glass for the benchmarkExample 7 is calculated based on the peak area from FIG. 2 to be 24.2percent. The grease-like transfer factor is calculated as the percenttransfer of a particular additive divided by the percent transfer of thebenchmark additive. The benchmark additive is the commercial grade GMS,so the greasiness factor for this particular GMS is 1.0. The percentreduction in grease-like transfer is reported in Column 8 of Table 2.

[0052] Example 1 was with the same GMS additive used in Example 7, butat a 0.4 percent concentration rather than at a 1.2 percentconcentration. The grease-like transfer factor, expressed as apercentage of greasiness, was only 66 percent for a 16.1 percenttransfer of additive from foam to glass, which shows that the amount ofgrease-like transfer of an additive is also dependent upon theconcentration of the additive in the resin from which the foam is made.FIG. 3 shows the effect of concentration of process additive in a plotof absorbance versus wavenumber for GMS at various concentrations.

[0053] Table 2 shows clearly that the use of compounds E and F asprocess additives, which are steaamide and lauramide MEA, respectively,produces a superior grease-like transfer factor with low percenttransfer of the additive to the glass and a high reduction ingrease-like characteristics.

[0054] The greasiness factor calculated for various compounds atdifferent concentrations is shown graphically in FIG. 4 with the GMSadditive of FIG. 2 and Example 7 as the benchmark having a grease-liketransfer factor of 1. The Alkamide S-280 additive of Example 8 is shownto have a grease-like transfer factor of only 6 percent by comparison tothe GMS aging modifier of Example 2. Alkamide L-203 as shown in Examples10 and 11 also has low grease-like transfer factor.

[0055] Kemamide S-280 (C, Table 1) is shown in FIG. 4 to have agrease-like transfer factor of 31 percent and Kemamide S (D, Table 1)has been determined to have a similar grease-like transfer factor whencompared to GMS. Kemamide S-280 and Kemamide S are secondary and primaryaliphatic amides, respectively, and do not include an alcohol moiety asdo the process additives of the invention. Kemamide S-280 and S inadmixture with GMS show two distinct melting points, one for the amideand one for the ester, which does not indicate chemical interactionbetween these amides and GMS. While not wishing to be bound by theory,it is believed that Kemamide S-180 and Kemamide S merely dilute thegreasines transfer factor for GMS, in distinction to compounds E and Fof the invention, as shown in Table 2 and in FIG. 4 (Alkamide S-280 andAlkamide L-203, respectively).

[0056]FIG. 5 is a plot of grease-like transfer factor versusconcentration for GMS and shows that the grease-like transfer factorincreases with increasing concentration based on Examples 4, 5, and 6 ofTable 2.

[0057] Table 3 shows 13 examples of various low density polyethyleneresins used to prepare lightweight foams with various process additives.Examples 12 through 15 use a concentration of 1.3 percent by weight of acommercial GMS as the benchmark examples. Examples 16 through 22 areprepared with a mixture comprising 60 percent GMS and 40 mole percentAlkamide S-280. This mixture exhibits a single melting point of 72°Centigrade, which is some 12° Centigrade above the melting point for acommercial GMS, which is compound B, Table 1. The single melting pointis thought to signify some chemical interaction between the components.Example 23 is prepared with 1 percent percent GMS and 1.3 percent SAPDby weight. The total amount of the process additive is accordingly by2.3 percent by weight of the resin and comprises 44 percent GMS and 56percent SAPD. Example 24 is prepared with 0.5 percent percent GMS and0.5 percent SAPD by weight for a 50/50 blend of GMS and SAPD at 1percent of the resin by weight.

[0058] As can be seen, the standard FT-IR test shows that thegrease-like transfer level of the foams was substantially reduced oreliminated as compared to GMS used alone. The foam samples of Table 3were evaluated by heating in an oven at 40° centigrade for 24 hours incontact with KBr glass windows. Negligible levels of grease-liketransfer were achieved when GMS was mixed with stearyl monoethanolamide(stearamide MEA). TABLE 3 Thickness, Foam Aging Modifier % % GreasinessPeak Example inches Density, pcf wt. percent Transfer Level# Area 120.95  1.22 1.3% A 21.8 90.0% 1.210 13 0.112 1.10 1.3% A 21.6 89.2% 1.20014 0.085 1.29 1.3% A 23.6 97.5% 1.313 15 0.101 1.27 1.3% A 36.6 151.2%2.035 16 0.119 1.17 1.7% A/E mix† 0.9 3.7% 0.050 17 0.125 1.07 1.7% A/Emix 1.3 5.8% 0.075 18 0.099 1.06 1.7% A/E mix 1.3 5.8% 0.075 19 0.0591.3  1.7% A/E mix 0.7 2.9% 0.038 20 0.065 1.26 1.7% A/E mix 0.9 3.7%0.050 21 0.060 1.21 1.1% A/E mix <0.7 <2.5* <.03 22 0.060 1.40 1.5% A/Emix 4.9 19.6 .25 23 0.092 1.36 2.3% A/H mix** 7.3 30.3 .40 24 0.095 1.371.0% A/H mix ## 7.2 30.0 .40

[0059]FIG. 6 shows a plot for Examples 12 through 20 of Table 3 ofabsorbance versus wavenumber, which gives an indication of thegrease-like transfer properties of the foam product. Examples 16, 17,18, 19, and 20, which are examples of the invention, show negligiblegrease-like transfer properties and virtually no peak.

[0060] Table 4, below, shows nine examples of the use of variouscompounds as process additives in thin foam sheets. Example 26 is thecontrol example in which 1.3 percent of GMS was used as the processadditive. Examples 27, 28, and 29, which are examples of the invention,show a mixture comprising 1.3 percent GMS with from 0.6 to 0.8 percentstearamide MEA. Examples 27 through 29 show a clean foam withsubstantially no grease-like transfer visible to the unaided eye. Theresults for each of these five examples is plotted in FIG. 7.

[0061] Examples 30 through 33 are also examples of the invention.Example 30 is similar to Examples 27 through 29 and shows a clean foamwith substantially no detectable grease-like transfer. Examples 31, 32,and 33 show a mixture of GMS and Alkamide LIPA (Example 31) and SAPD(Examples 32 and 33) in the volume percentages shown in Table 4 for eachingredient. These additives resulted in foams that are only sightlygreasy and have a low transfer percentage compared to GMS alone. TABLE 4Foam Aging Density, % Greasiness % Visual Example Modifier pcf (fromFT-IR) Transfer Comments 25 1.3% A 1.17 20.7 86.6 Greasy 26 1.3% A 1.3523.9 100 Greasy 27 A/E mix† 1.19 1.7 4.9 Clean, greaseless 28 A/E mix1.74 1.1 4.6 Clean, greaseless 29 A/E mix 1.55 1.1 4.6 Clean, greaseless30 1.1% A/E 1.2 <0.7 <2.5 Clean mix 31 1.5% A/G 1.4 4.9 19.6 Slightlymix* Greasy 32 2.3% A/H 1.36 7.3 30.3 Slightly mix# Greasy 33 1% A/H1.37 7.2 30.0 Slightly mix** Greasy

[0062] The fatty acid N-aliphatic alcohol amide provides suprisinglyexcellent results in the reduction of grease-like transfer in lowdensity foams as compared to traditional aging modifiers such as a GMS.However, as observed above, when used in admixture, GMS and the fattyacid N-aliphatic alcohol amide can produce an even greater reduction ingrease-like transfer from foams. The addition of a small amount of thefatty acid N-aliphatic alcohol amide to a GMS process additive canproduce significant reduction in the grease-like transfercharacteristics of a foam.

[0063] The two compounds exhibit a single melting point when used inadmixture, which signifies some chemical interaction and may beresponsible for the improved results. The single melting point that isexhibited by the mixture of the amide and the ester varies depending onthe ratio of the ester to the amide and the aging modifier. The meltingpoint decreases linearly as the ratio of the ester to the amideincreases.

[0064] GMS has the structure of an ester of a long chain fatty acid witha polyhydric alcohol. Other esters of long chain fatty acids withpolyhydric alcohols have similar properties and should be useful in thepractice of the invention. Typically, the ester will be a glyceride, andsomewhat more typically, a monoglyceride. The polyhydric alcohol thatcomprises the ester typically will be a trihydric alcohol. Where theester is glycerol stearates, the glycerol monostearate can be eitheralpha glycerol monostearate, beta glycerol monostearate, or mixturesthereof with glycerol di- or tri-stearates. Typically, the ester shouldbe present in the aging modifier in a ratio of the ester to the fattyacid N-aliphatic alcohol amide of from about 0:1 to 10:1.

[0065] The GMS and fatty acid N-aliphatic alcohol amide components arepresent in the aging modifier in a ratio of the GMS to the amide of fromabout 0:1 to 10:1. A ratio of the ester to the amide of about 2:1 isuseful.

[0066] The foams are prepared by incorporating the aging modifiercomponents in a polymeric composition and then expanding the polymericcomposition. The polymeric composition will normally comprise apolyolefinic resin. The polyolefinic resin can be formed from ethyleneor propylene homopolymers or copolymers of ethylene or propylene and acopolymerizable monomer. The aging modifier will typically be present inthe polymeric composition in a ratio of the polyolefin resin of theaging modifier of from about 100:0.01 to 100:5. A ratio of a polyolefinto aging modifier of about 100:0.5 to 100:3 may be somewhat moretypical.

[0067] The polymeric composition will also comprise a blowing agent. Anyof the blowing agents known in the art should be useful in the practiceof the invention. However, it normally is not desirable to use thoseblowing agents that are being phased out because of governmentalregulation. The blowing agent typically will be an inert gas or ahydrocarbon having from 1 to 6 carbons, or mixtures thereof. Any of theinert gases and hydrocarbon blowing agents should be useful in thepractice of the invention, including carbon dioxide, either alone or inan admixture with a hydrocarbon blowing agent. The process additive ofthe invention is particularly useful in part because the additivepromotes an increased rate of blowing agent escape from the cells of thefoam as compared to GMS alone. Thus, aging time is reduced and foamstability is promoted.

[0068]FIGS. 8 and 9 show reduced aging times for foams of the invention.FIGS. 8 and 9 are plots of the percentage of the lowest explosive limit(% LEL) over time for two different blowing agents for polyethylene foamprepared with a process additive of the invention. The % LEL is ameasure of the least amount of a hydrocarbon dispersed in air that isexplosive if exposed to a spark or flame. It is desirable to reduce the% LEL to acceptably low values below 100% prior to storing the foam in aconfined space.

[0069] The blowing agents were 100% propane and a blend of about 75%propane and 25% carbon dioxide. Rolls of expanded sheet foam preparedwith these blowing agents in accordance with the invention were aged ina warehouse, as described below. The aged foams were placed in a trailerof the type in which the foams are commonly transported by a tractor andtrailer combination. The trailer was 35 feet long and was filled to 85%of capacity to simulate actual loading conditions. The test was staticin that the trailer did not move. Once in travel, the free flow of airthrough a trailer tends to reduce the % LEL as compared to staticconditions.

[0070] The % LEL was determined over time inside the trailer at 6 inchesabove the bottom of the trailer, since propane is heavier than air. The% LEL is plotted in FIGS. 8 and 9 against time, temperature, andhumidity for each of the blowing agents. As is shown in the plots ofFIGS. 8 and 9, in all cases the % LEL remains below 16%. FIG. 8 is atthe trailer nose; FIG. 9 is at the center.

[0071] The foam sheets were prepared on a production system having aprimary extruder of diameter 8.9 cm and a secondary extruder of diameter11.4 cm. A resin of low density polyethylene “LDPE”) was foamed at arate of 205 kg/hr. An alcoholamide processing additive of the invention,stearamide monoethanolamine, was added at 0.63 kg/hr and GMS was addedat 1.47 kg/hr.

[0072] The fresh rolls of foam sheet prepared with 100% propane blowingagent were aged in a warehouse for 6 days. Normally, aging could beexpected to take from about 10 to 12 days to reduce the lowest explosivelimit to acceptable levels for foams prepared from GMS alone and a 100%propane blowing agent. The % LEL is desirably reduced at least to about50%. As can be seen in FIGS. 8 and 9, the % LEL for the propane foam wasfrom less than 12 to about 16 at the beginning of the trailer test andafter only 6 days of warehouse aging, and remained even lowerthereafter.

[0073] Unlike volatile hydrocarbons, carbon dioxide based blowing agentstypically escape so quickly from foam that problems of collapse aresomewhat common. However, the processing additive of the invention iscapable of producing stable, high quality polyolefin foams of reducedaging time from carbon dioxide blowing agents.

[0074] It is generally useful to mix the carbon dioxide with ahydrocaron having from 1 to 6 carbons, or mixtures thereof. For theplots of FIGS. 8 and 9, LDPE foam sheet of the invention was preparedwith a blowing agent mixture of 27% of carbon dioxide and 73% propane,by weight. It should be recognized that “mixture” does not necessarilymean the carbon dioxide and propane were physically mixed prior toadding to the polyolefin resin, although premixing can be accomplishedif desired.

[0075] In the examples of FIGS. 8 and 9, carbon dioxide was added at therate of 5.1 kg/hr and propane was added separately at a rate of 15.6kg/hr. The solution of polymer melt and gas was cooled to less than 110°C. and expanded through an annular die orifice to form a sheet. The foamhad a density of 17.6 kg/cubic meter and was 3.2 mm thick. The sheet waswound on a roll for storage and was aged in a warehouse for 2 days priorto the trailer test. On the third day, the foam was placed in thetrailer. The % LEL during the trailer test never rose above about 5 to10%.

[0076] The combination of carbon dioxide and volatile hydrocarbonblowing agent is particularly advantageous when practiced in connectionwith the preparation of foams from resins having the processing additiveof the invention. These foams have excellent stability and significantlyreduced aging time as compared to foams prepared using GMS alone as aprocessing additive.

[0077] The above invention has been described with respect to particularpreferred embodiments. However, the foregoing description is notintended to limit the invention to the illustrated embodiments and theskilled artisan should recognize that variations can be made within thespirit and scope of the invention as described in the foregoingspecification. The invention includes all alternatives, modifications,and equivalents that may be included within the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A film comprising a polyolefin, at least onefatty acid N-aliphatic alcohol amide, wherein the amide is secondary ortertiary, and an ester of a long chain fatty acid with a polyhydricalcohol, wherein said ester and said amide are present in said film in aratio of said ester to said amide of from about 0:1 to 10:1.
 2. The filmof claim 1 wherein said ester and said amide have a substantially singlemelting point that varies depending upon the ratio of said ester to saidamide.
 3. The film of claim 1 wherein said amide is a secondary amide.4. The film of claim 1 wherein said amide is a fatty monoalkanol amide.5. The film of claim 1 wherein the fatty acid portion of said amide hasfrom about 8 to 30 carbons.
 6. The film of claim 1 wherein the fattyacid portion of said amide is selected from the group consisting ofcoconut, lauric, palmitic, stearic, and oleic moieties.
 7. The film ofclaim 1 wherein the aliphatic alcohol portion of said amide is amonohydric alkyl alcohol moiety of from about 1 to 6 carbons.
 8. Thefilm of claim 7 wherein said monohydric alkyl alcohol moiety is selectedfrom the group consisting of methanol, ethanol, propanol, butanol,pentanol, and hexanol moieties, and isomers thereof.
 9. The film ofclaim 1 wherein the aliphatic alcohol portion of said amide is apolyhydric alcohol moiety of from about 1 to 6 carbons with from 2 to 5hydroxyl moieties.
 10. The film of claim 9 wherein said polyhydricalcohol moiety is a glycol radical.
 11. The film of claim 1 wherein saidamide is selected from the group consisting of fatty monoethanolamide,fatty 2,3-propanediol amide, and fatty isopropanol amide.
 12. A filmcomprising a polyolefin, an ester of a long chain fatty acid with apolyhydric alcohol, and a molecule having the formula R—CON(R)R″,wherein R is a fatty alkyl radical having from about 8 to 30 carbons, R′is selected from the group consisting of hydrogen, an alkyl radical offrom about 1 to 6 carbons, and an alkyl alcohol radical of from about 1to 6 carbons, and R″ is a mono or polyhydric alcohol radical of fromabout 1 to 6 carbons; wherein said ester and said amide are present insaid film in a ratio of said ester to said amide of from about 0:1 to10:1.
 13. The film of claim 12 wherein R′ and R″ are selected from thegroup consisting of monohydric alkyl alcohol radicals, polyhydric alkylalcohol radicals, and mixtures thereof.
 14. The film of claim 12 whereinR′ is hydrogen and R″ is selected from the group consisting of methanol,ethanol, propanol, butanol, pentanol, and hexanol radicals, isomersthereof, and mixtures thereof.
 15. The film of claim 12 wherein saidester is glycerol monostearate.
 16. The film of claim 23 wherein saidester is a mixture of glycerol mono-, di-, and tri-stearates.
 17. Thefilm of claim 23 wherein said ester and said molecule of claim 12 arepresent in a ratio of said ester to said molecule of about 2:1.
 18. Aprocess additive for polyolefins comprising at least one fatty acidN-aliphatic alcohol amide, wherein the amide is secondary or tertiary,and an ester of a long chain fatty acid with a polyhydric alcohol,wherein said ester and said amide are present in said process additivein a ratio of said ester to said amide of from about 0:1 to 10:1. 19.The process additive of claim 18 having a substantially single meltingpoint that varies depending upon the ratio of said ester to said amidein said aging modifier.
 20. The process additive of claim 18 whereinsaid amide is a secondary amide.
 21. The process additive of claim 18wherein said amide is a fatty monoalkanol amide.
 22. The processadditive of claim 18 wherein the fatty acid portion of said amide hasfrom about 8 to 30 carbons.
 23. The process additive of claim 18 whereinthe fatty acid portion of said amide is selected from the groupconsisting of coconut, lauric, palmitic, stearic, and oleic moieties.24. The process additive of claim 38 wherein the aliphatic alcoholportion of said amide is a monohydric alkyl alcohol moiety of from about1 to 6 carbons.
 25. The process additive of claim 24 wherein saidmonohydric alkyl alcohol moiety is selected from the group consisting ofmethanol, ethanol, propanol, butanol, pentanol, and hexanol moieties,and isomers thereof.
 26. The process additive of claim 18 wherein thealiphatic alcohol portion of said amide is a polyhydric alcohol moietyof from about 1 to 6 carbons with from 2 to 5 hydroxyl moieties.
 27. Theprocess additive of claim 26 wherein said polyhydric alcohol moiety is aglycol radical.
 28. The process additive of claim 18 wherein said amideis selected from the group consisting of fatty monoethanolamide, fatty2,3 dihydroxy propyl amide, and fatty isopropanol amide.
 29. A processadditive for polyolefins comprising an ester of a long chain fatty acidwith a polyhydric alcohol and a molecule having the structure R—CON(R)R″wherein R is a fatty hydrocarbon radical having from about 8 to 30carbons, R′ is selected from the group consisting of hydrogen, an alkylradical of from about 1 to 6 carbons, and an alkyl alcohol radical offrom about 1 to 6 carbons, and R″ is an alkyl alcohol radical of fromabout 1 to 6 carbons, wherein said ester and said molecule are presentin said process additive in a ratio of said ester to said amide of fromabout 0:1 to 10:1.
 30. The process additive of claim 29 wherein saidmolecule is stearamide monoethanolamine.
 31. A polyolefinic compositioncomprising polyolefin, a gaseous blowing agent, at least one fatty acidN-aliphatic alcohol amide, wherein the amide N is secondary or tertiary,and an ester of a long chain fatty acid with a polyhydric alcohol,wherein said ester and said amide are present in said composition in aratio of said ester to said amide of from about 0:1 to 10:1.
 32. Thecomposition of claim 31 wherein said gaseous blowing agent is ahydrocarbon having from 1 to 6 carbons.
 33. The composition of claim 31wherein said gaseous blowing agent is propane.
 34. The composition ofclaim 31 wherein said gaseous blowing agent comprises carbon dioxide anda hydrocarbon having from 1 to 6 carbons.
 35. The composition of claim31 wherein said gaseous blowing agent comprises about 25% carbon dioxideand about 75% hydrocarbon.
 36. The composition of claim 31 wherein saidester and said amide are present in said composition in a ratio of saidester to said amide of about 2:1
 37. A polyolefinic compositioncomprising low density polyolefin, a gaseous blowing agent comprisingcarbon dioxide, glycerol monostearate, and stearamide monoethanolamine,wherein said ester and said amide are present in said composition in aratio of said ester to said amide of about 2:1.
 38. A process forproducing polyolefinic foams comprising blending a plasticizedpolyolefin resin with a gaseous blowing agent under pressure andextruding the resin and blowing agent into a zone of reduced pressure toproduce a foam, wherein the resin comprises at least one fatty acidN-aliphatic alcohol amide, wherein the amide N is secondary or tertiary,and an ester of a long chain fatty acid with a polyhydric alcohol, andwherein said ester and said amide are present in said composition in aratio of said ester to said amide of from about 0:1 to 10:1.
 39. Theprocess of claim 38 wherein the blowing agent comprises carbon dioxide.40. The process of claim 39 wherein the blowing agent further compriseshydrocarbon.
 41. The process of claim 40 wherein the hydrocarbon hasfrom 1 to 6 carbons.
 42. The process of claim 41 wherein the hydrocarbonis propane.
 43. The process of claim 42 wherein the propane is presentin an amount of about 75% by weight and the carbon dioxide is present inan amount of about 25% by weight and wherein said ester and said amideare present in said composition in a ratio of said ester to said amideof from about 2:1.
 44. A polyolefinic foam comprising polyolefin and agaseous blowing agent comprising volatile hydrocarbon, wherein the % LELin a confined space and under static conditions is reduced below 50%after 2 days (48 hours) of aging time.